1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device which is provided with a backlight on a rear surface of a liquid crystal panel, is light-weighted and can cope with the reduction in picture frame.
2. Description of the Related Art
A liquid crystal display device has been widely used as a high-definition color display device for a notebook type computer or a computer monitor. Such a liquid crystal display device which enables the high definition color display for the notebook type computer or the computer monitor is provided with a light source which illuminates a liquid crystal panel from a rear surface thereof (so-called backlight).
This type of liquid crystal display device is basically constituted of a so-called liquid crystal panel which inserts a liquid crystal layer between two sheets of substrates wherein at least one of the substrates is made of a transparent substrate such as a glass plate or the like. The liquid crystal display device is roughly classified into a system which performs turning on and off of given pixels by selectively applying voltages to respective electrodes for forming pixels which are formed on the above-mentioned substrate of the liquid crystal panel (simple matrix) and a system which forms the above-mentioned respective electrodes and active elements for selecting pixels and performs turning on and off of given pixels by selecting these active elements (active matrix).
As an active matrix type liquid crystal display device, a so-called vertical electric field type (for example, see Japanese Patent Laid-Open No. 309921/1988) which applies an electric field between pixel electrodes formed on one substrate and common electrodes formed on the other substrate for changing the orientation direction of a liquid crystal layer and a so-called lateral electric field type (also referred to as IPS type) which makes the direction of an electric field applied to a liquid crystal layer arranged in the direction approximately parallel to a surface of a substrate are known.
As the liquid crystal display device of the lateral electric field type, a liquid crystal display device which can obtain an extremely wide viewing angle by using comb-teeth electrodes on one of two sheets of substrates is known (see Japanese Patent Laid-Open No. 21907/1988, U.S. Pat. No. 4,345,249).
In either one of the above-mentioned liquid crystal display device as an illumination source of the liquid crystal panel, there has been known a side-edge type backlight which is constituted of a light guide plate and linear lamp or a direct backlight which arranges a plurality of linear light sources such that they directly face a rear surface of the liquid crystal panel in an opposed manner.
Particularly, the backlight of side-edge type is constituted such that the linear lamp (usually cold-cathode fluorescent lamp CFL) is arranged along at least one side periphery of a transparent plate such as an acrylic plate or the like, light emitted from the linear lamp is introduced into the light guide plate and the path of the light is changed in the course of its propagation in the inside of the light guide plate so as to illuminate the liquid crystal panel disposed above the light guide plate from the rear surface of the panel.
Further, recently, along with the popularization of multimedia and mobile computing, the popularization of a notebook type personal computer or a handy terminal or the like having functions comparable with functions of a desktop type computer has been in progress. As a display device of such equipment, a screen device having a large screen of a size of 14–15 inches has been currently commercialized in the notebook type personal computer. Further, in the personal computer of desktop type or the like, a monitor having a large screen of 17–20 inches or more which uses a liquid crystal panel has been requested and they have been actually commercialized. Further, in the handy terminal, a liquid crystal display device of a reflection type is used in many cases.